I imagine there's a scholarly article in how warchalking went from the brain of Matt Jones into the public noösphere and then was entirely commodified: Warchalking was supposed to be a way for folks to tag locations with open or closed marks--even a way to advertise that you were offering Wi-Fi as an individual.
The only time I've ever seen a warchalk symbol has been on a business card or a piece of corporate signage. My editorial and advertising partner JiWire built the warchalk symbol into their logo.
Now the ultimate step is Krystal's restaurant, which is adding free Wi-Fi to 243 corporate stores and as many of the 180 franchisees who will pony up for it. Their symbol?